Solid-state imaging device, method of producing the same, and camera

ABSTRACT

To provide a solid-state imaging device able to improve light transmittance of a transparent insulation film in a light incident side of a substrate, suppress the dark current, and prevent a quantum efficiently loss, wherein a pixel circuit is formed in a first surface of the substrate and light is received from a second surface, and having: a light receiving unit formed in the substrate and for generating a signal charge corresponding to an amount of incidence light and storing it; a transparent first insulation film formed on the second surface; and a transparent second insulation film formed on the first insulation film and for retaining a charge having the same polarity as the signal charge in an interface of the first insulation film or in inside, thicknesses of the first and second insulation film being determined to obtain a transmittance higher than when using only the first insulation film.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.12/662,982, filed May 14, 2010, which is a Divisional Application ofU.S. patent application Ser. No. 11/181,748, filed Jul. 15, 2005, nowU.S. Pat. No. 7,737,520, issued Jun. 15, 2010, which in turn claimspriority from Japanese Patent Application No. JP 2004-233760 filed inthe Japanese Patent Office on Aug. 10, 2004, the entire contents ofwhich being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a back illumination type (backilluminated) solid-state imaging device receiving light from an oppositeside to a surface formed with a pixel circuit, a method of producing thesame, and a camera including the same.

2. Description of the Related Art

There is known, for example, front illumination type (front illuminated)solid-state imaging devices in which a light receiving unit and a readout transistor are placed with in a pixel, so, in a CCD type solid-stateimaging device and a CMOS type solid-state imaging device, an area forthe light receiving unit is restricted. For an enlargement of the areafor the light receiving unit, in the CCD or CMOS type solid-stateimaging device, an on-chip lens or a multilayered light receiving unitusing photoconductive film has been employed. Also, in the CCD typesolid-state imaging device, a frame transfer CCD using a transparentelectrode or a thin polysilicon electrode has been employed.

In above configurations, an effective aperture area of the lightreceiving unit is enlarged to improve light sensitivity. As a pixel issmaller, an eclipse of incidence light is obviously by a pixelinterconnection and a transfer gate electrode unit. Therefore, a backilluminated (back illumination type) solid-state imaging device has beenexpected as a configuration for high-sensitivity of the light receivingunit. As the back illuminated solid-state imaging device, a CCD type isdiscloses by Japanese Unexamined Patent Publication (Kokai) No.2002-151673, and a MOS type is discloses by Japanese Unexamined PatentPublication (Kokai) No. 2003-31785. In the back illuminated solid-stateimaging device, a frame transfer (FT) type or a frame interline transfer(FIT) type has been employed.

In the case of the CCD type and the MOS type, a p-type silicon substrateis used as a substrate. For example, Japanese Unexamined PatentPublication (Kokai) No. 6-350068 discloses the following threestructures for suppressing a dark current at an interface of a backsurface, namely a light incident surface.

A first structure is formed with a p⁺-layer with high concentration atthe back surface to suppress a depletion at the back surface. A secondstructure is formed with a transparence electrode via an insulation filmat the back surface. A negative voltage is supplied to the transparentelectrode to make a hole storage state in the back surface of asubstrate. A third structure is injected with negative charges at aninsulation film formed at the back surface of the substrate to make thehole storage state in the back surface of the substrate due to thenegative charge.

SUMMARY OF THE INVENTION

In the above document, a silicon oxide film is formed as a reflectionprevention film in a back surface of a substrate and p-type impuritiesare injected via the silicon oxide film by ion implantation. However,the silicon oxide film only has a transmittance of 75 to 80% in average.Namely, a light loss of 20 to 25% occurs to reduce the lightsensitivity.

The present invention is to provide a solid-state imaging device able toimprove light transmittance of a transparent insulation film at a lightincident side of a substrate, suppress a dark current, and prevent aquantum efficiently loss, and a method of producing the same and acamera including the same.

According to an embodiment of the present invention, there is provided asolid-state imaging device in which a pixel circuit is formed in a firstsurface side of a substrate and light is received from a second surfaceside, the solid-state imaging device having: a light receiving unitformed in the substrate and for generating a signal charge correspondingto an amount of incidence light and storing the signal charge; atransparent first insulation film formed on the second surface of thesubstrate; and a transparent second insulation film formed on the firstinsulation film and for retaining a charge having the same polarity asthe signal charge in an interface of the first insulation film or ininside. Thicknesses of the first insulation film and the secondinsulation film are determined to obtain a transmittance of theincidence light higher than when using only the first insulation film.

According to an embodiment of the present invention, there is provided amethod of producing a solid-state Imaging device having the steps of:forming a light receiving unit and a pixel circuit in a first surfaceside of a substrate; grinding a second surface side of the substrate tomake the substrate thinner; forming a transparent first insulation filmon the second surface of the substrate; forming a second insulation filmon the first insulation film; and injecting charges having the samepolarity as a signal charge in an interface between the first insulationfilm and the second insulation film or in the second insulation film. Inthe steps of forming the first insulation film and the second insulationfilm, the first insulation film and the second insulation film areformed to have thicknesses so as to obtain a transmittance of anincidence light higher than when using only the first insulation film.

According to an embodiment of the present invention, there is provided amethod of producing a solid-state imaging device comprising the stepsof: forming a light receiving unit and a pixel circuit at a firstsurface side of a substrate having a first insulation film; grinding asecond surface side of the substrate to expose the first insulationfilm; forming a second insulation film on the first insulation film; andinjecting charges having the same polarity as a signal charge in aninterface between the first insulation film and the second insulationfilm or in the second insulation film. In the steps of forming the firstinsulation film and the second insulation film, the first insulationfilm and the second insulation film are formed to have thicknesses so asto obtain a transmittance of an incidence light higher than when usingonly the first insulation film.

According to an embodiment of the present invention, there is provided acamera having: a solid-state imaging device in which a pixel circuit isformed in a first surface side of a substrate and light is received froma second surface side; an optical system focusing light on the secondsurface of the solid-state imaging device; and a signal processingcircuit performing a predetermined signal processing to an output signalfrom the solid-state imaging device. The solid-state imaging signalincludes: a light receiving unit formed in the substrate and forgenerating a signal charge corresponding to an amount of incidence lightand storing the signal charge; a transparent first insulation filmformed on the second surface of the substrate; and a transparent secondinsulation film formed on the first insulation film, and for retaining acharge having the same polarity as the signal charge in an interface ofthe first insulation film or inside. The thicknesses of the firstinsulation film and the second insulation film are determined to obtaina transmittance of the incidence light higher than when using only thefirst insulation film.

According to a solid-state imaging device, a method of producing thesame, and a camera of an embodiment of the present invention, it is ableto improve light transmittance of a transparent insulation film at alight incident side of a substrate, suppress a dark current, and preventa quantum efficiently loss.

BRIEF DESCRIPTION OF THE DRAWINGS

These features of embodiments of the present invention will be describedin more detail with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a light receiving unit of asolid-state imaging device according to the present embodiment;

FIGS. 2A and 2B are cross-sectional views of a process for producing thesolid-state imaging device according to the present embodiment;

FIG. 3 is a cross-sectional view of a process for Producing thesolid-state imaging device according to the present embodiment;

FIGS. 4A and 4B are cross-sectional views of a process for producing thesolid-state imaging device according to the present embodiment;

FIG. 5A is a view showing an energy band in the vicinity of a backsurface of a semiconductor substrate of a comparative example, and FIG.5B is a view showing an energy band in the vicinity of a back surface ofa semiconductor substrate of the present embodiment;

FIGS. 6A and 6B are views showing transmittance of a structure of thecomparative example;

FIGS. 7A and 7B are views showing transmittance of a structure of thepresent embodiment;

FIG. 8 is a view showing a transmittance of blue light and green lightwhen employing various thicknesses of a silicon oxide and a siliconnitride; and

FIG. 9 is a view of a configuration of a camera according to the presentembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings. The present invention can beapplied to a CCD type solid-state imaging device and a MOS typesolid-state imaging device.

FIG. 1 is a view of an elementally portion in a light receiving unit ofa solid-state imaging device according to the present embodiment.

In the present embodiment, a semiconductor substrate 1 of, for example,p-type silicon, is used. The thickness of the semiconductor substrate 1depends on a kind and an application of the solid-state imaging device,and is preferably 4 to 6 μm for visible light or 6 to 10 μm fornear-infrared radiation.

In the semiconductor substrate 1, an n-type semiconductor region 2 and ap-type semiconductor region 3 are formed in the respective pixels. Then-type semiconductor region 2 substantially stores signal chargesconverted from light in the semiconductor substrate 1.

The p-type semiconductor region 3 is formed at a first surface side(surface side) nearer than the n-type semiconductor region 2, andcontains p-type impurities with higher concentration than thesemiconductor substrate 1. The p-type semiconductor region 3 prevents adepleted layer generated between the n-type semiconductor region 2 and ap-type region around the n-type semiconductor region 2 from reaching asurface of the semiconductor substrate 1 to suppress a dark current andimprove a quantum efficiency.

A light receiving unit 4 is a buried photo diode including the aboven-type semiconductor region 2 and the p-type semiconductor region 3. Thelight receiving unit 4 stores a signal charge in the n-typesemiconductor region 2 temporary.

On the first surface side of the semiconductor substrate 1, an electrode6 included in a pixel circuit is formed via an insulation layer 5, forexample, which is made of silicon. The electrode 6 is covered with aninterlayer insulation layer 7, for example, which is made of siliconoxide.

In case of the CCD type solid-state imaging device, a CCD verticaltransfer resistor is included in the pixel circuit. In this case, theelectrode 6 corresponds to, for example, a transfer electrode of the CCDvertical transfer resistor, and a transfer channel of the n-type regionis formed in the semiconductor substrate 1 beneath the electrode 6.

In case of the MOS type solid-state imaging device, a read outtransistor, an amplifying transistor, a reset transistor, an addresstransistor, or other transistors are included in the pixel circuit. Inthis case, the electrode 6 corresponds to, for example, a gate electrodeof various transistors, and source/drain regions of various transistorsand a floating diffusion are formed in the semiconductor substrate 1.

Since the semiconductor substrate 1 is made thin at about 4 to 10 μm, asupporting substrate may be formed on the interlayer insulation film 7.In order to prevent an occurrence of a warp caused by a difference froma thermal expansion coefficient of the semiconductor substrate 1, as thesupporting substrate, a silicon substrate which is the same as thesemiconductor substrate 1 is used preferably.

At a second surface side (back surface) of the semiconductor substrate1, a transparent first insulation film and a transparent secondinsulation film having a refractive index higher than the firstinsulation film are formed. In the present embodiment, a silicon oxidefilm 8 is formed as the first insulation film and a silicon nitride film9 is formed as the second insulation film.

The thicknesses of the silicon oxide film 8 and the silicon nitride film9 are adjusted to obtain a high transmittance to the incidence light dueto a multiple interference effect of light in comparison with using onlythe silicon oxide film 8.

The thickness of the silicon oxide film 8 is 15 to 40 nm, and thethickness of the silicon nitride film 9 is 20 to 50 nm. In these ranges,the respective thicknesses are optimized to obtain the hightransmittance to the incidence light in comparison with using only thesilicon oxide film 8.

Charges which is the same polarity as the signal charge, for example,electrons in the present embodiment, are injected in the silicon nitridefilm 9 or in an interface between it and the silicon oxide 8. Thereasons employing the silicon nitride film 9 are described as thefollowings. First, as employed to MONOS or other nonvolatile memory, thesilicon nitride film has a good charge retention characteristic. Second,since the refractive index of the silicon nitride is higher than that ofthe silicon oxide film 8, by adjusting the thickness, a transmittance tothe incidence light is obtained higher than only using the silicon oxidefilm 8 due to the multiple interference effect.

Since the electrons are stored in the silicon nitride 9, a hole storagelayer 10 including a lot of holes h is generated in the vicinity of theinterface between the semiconductor substrate 1 and the silicon oxidefilm 8 in the semiconductor substrate 1. Due to the hole storage layer10, the occurrence of the dark current and the quantum effect loss areprevented as described below.

On the silicon nitride film 9, a protection film 11 is formed, whichprevents the electrons stored in the silicon nitride film 9 from passingthe outside to disappear. As the protection film 11, it is preferablymaterials with a low refractive index and low light absorption forvisible light. Most of transparent resin films which are generally usedfor a semiconductor device can be used, and also a silicon oxide filmformed by low temperature plasma CVD and a silicon oxide-nitride filmformed by the similar way may be used.

Next, a method for producing a solid-state imaging device according tothe present embodiment will be described with reference to FIGS. 2A and2B, FIG. 3, and FIGS. 4A and 4B. In the present embodiment, an exampleproducing the solid-state imaging device by using, for example, an SOIsubstrate will be described.

First, as shown in FIG. 2A, an SOI substrate having the semiconductorsubstrate (SOI layer) 1 made of P-type silicon, the silicon oxide film8, and the silicon substrate 12 are prepared. Here, the thickness of thesilicon oxide film 8 is adjusted in 15 to 40 nm. Then, the lightreceiving unit and the pixel circuit are formed at the first surface(front surface) side of the semiconductor substrate 1 by a similar wayto the related art.

Namely, the n-type semiconductor region 2, the p-type semiconductorregion 3, and not shown various semiconductor regions are formed in thesemiconductor substrate 1 of the SOI substrate by the ion implantation.Then, the insulation layer 5 made of a silicon oxide film is formed,further the electrode 6 is formed. The electrode 6 is made of tungstenor aluminum. After a formation of the electrode 6, silicon oxide isdeposited to form the interlayer insulation film 7. If necessary, a notshown supporting substrate is bonded on the interlayer insulation film7, and then the silicon substrate 12 is grinded and etched to expose thesilicon oxide film 8.

Then, as shown in FIG. 2B, the front and back of the semiconductorsubstrate 1 are reversed, and the silicon nitride film 9 is formed onthe silicon oxide film 9 by plasma CVD. The thickness of the siliconnitride film 9 is selected in a range of 20 to 50 nm. Note that, if notusing the SOI substrate, the semiconductor substrate 1 may be made thin,then the silicon oxide film 8 and the silicon nitride film 9 may bedeposited successively.

Then, as shown in FIG. 3, for example, an electrode 20 charged to plusis opposed to the back surface (second surface) side of thesemiconductor substrate 1, then ultraviolet rays are irradiated to thesecond surface side of the semiconductor substrate 1. By the ultravioletrays, an electron e in the vicinity of the first surface of thesemiconductor substrate 1 is excited. The excited electron e jumps overthe silicon oxide film 8, and the excited electron e is trapped in theinterface of the silicon oxide film 8 and the silicon nitride film 9,and in the silicon nitride film 9. Due to an electric field generated bythe plus-charged electrode 20, the exited electron effectively jumpsover the silicon oxide film 8. Note that, only irradiating of theincident light or supplying the silicon oxide film 8 with an electricfield, the electrons can be injected in the interface between thesilicon oxide film 8 and the silicon nitride film 9 or in the siliconnitride 9.

As shown in FIG. 4A, the electrons are stored in the interface betweenthe silicon oxide film 8 and the silicon nitride film 9 and in thesilicon nitride film 9, consequently, in the semiconductor substrate 1made of p-type silicon, the hole is concentrated in the vicinity of theinterface of the silicon oxide film 8 to generate a hole storage layer10.

Then, as shown in FIG. 4B, the protection film 11 is formed on thesilicon nitride film 9. As described above, in the formation of theprotection film 11, for example, a coating of the transparent resinfilm, a deposition of the silicon oxide film by low temperature plasmaCVD, or a deposition of the silicon oxide nitride film by lowtemperature plasma CVD is performed.

As the following steps, if necessary, a color filter is formed on theprevention film 11, and an on-chip lens is formed. Therefore, thesolid-state imaging device is produced.

Next, an effect for preventions of the occurrence of the dark currentand the quantum efficient loss will be described.

Comparative Example

FIG. 5A is a view showing an energy band in the vicinity of the backsurface side of the semiconductor substrate 1 without the siliconnitride film 9. As shown in FIG. 5A, if silicon oxide is deposited onthe semiconductor substrate 1, plus charges may be generated easily inthe silicon oxide film 8 or in the interface between the semiconductorsubstrate 1 and the silicon oxide film 8. This applies to silicon oxideand other insulation films. As a result, a potential in the vicinity ofthe back surface of the semiconductor substrate 1 is raised to generatea potential-well. If the potential-well is formed in the vicinity of theback surface of the semiconductor substrate 1, electrons generated by aphotoelectric conversion may be also stored in the vicinity of the backsurface not to contribute the light sensitivity, and an occurrence of aminority carrier from the interface caused by heat may increase to raisethe dark current, consequently an S/N ratio of the imaging device isreduced.

Therefore, the semiconductor substrate 1 is preferably has a structurein which the interface of the silicon oxide film 8 is filled with holes.

FIG. 5B is a view showing an energy band in the vicinity of the backsurface (second surface) of the semiconductor substrate 1 in thesolid-state imaging device according to the present embodiment. In thepresent embodiment, since the electrons are stored in the interfacebetween the silicon oxide film 8 and the silicon nitride film 9 and inthe silicon nitride film 9, the hole storage layer is generated at theinterface of the back surface side of the semiconductor substrate 1. Asa result, a potential in the interface of the back surface side of thesemiconductor substrate 1 becomes reduced not to form the potential-wellin the vicinity of the interface.

In this way, the potential-well (portion with high potential) is notformed in the interface of the back surface of the semiconductorsubstrate 1, so the electrons generated by the photoelectric conversionare stored effectively in the n-type semiconductor region 2 with thehighest potential. The electrons stored in the n-type semiconductorregion 2 can be entirely read out or drained, so that the occurrence ofthe dark current can be suppressed and the quantum efficiency can beimproved.

Next, an effect which is obtained by improving the transmittance ofvisible light in the solid-state imaging device according to the presentembodiment will be described.

Comparative Example

As shown in FIG. 6A, as a comparative example, only the silicon oxidefilm 8 having the thickness of 2 μm is formed at the second surface sideof the semiconductor substrate 1. In a structure shown in FIG. 6A, aratio (transmittance) of a transmitted light TL to an incidence light Land a ratio (reflectance) of a reflected light RL to the incidence lightL are measured and the measured result will be shown in FIG. 6B. In FIG.6B, “T1” is a graph indicating the transmittance and “R1” is a graphindicating the reflectance.

As shown in FIG. 6B, if only the silicon oxide film 8 is formed in theback surface (second surface) of the semiconductor substrate 1, thetransmittance may be 75 to 80% in average in visible light, for example,450 to 740 nm.

FIG. 7A is a view of the measured result of the transmittance and thereflectance in the visible light when the silicon oxide film 8 havingthe thickness of 16 nm and the silicon nitride film 9 having thethickness of 40 nm are formed at the second surface side of thesemiconductor substrate 1. In FIG. 7A, “T2” indicates the transmittanceand “R2” indicates the reflectance.

FIG. 7B is a view of a measured result of the transmittance and thereflectance in the visible light when the silicon oxide film 8 havingthe thickness of 30 nm and the silicon nitride film 9 having thethickness of 35 nm are formed in the second surface side of thesemiconductor substrate 1. In FIG. 7B, “T3” indicates the transmittanceand “R3” indicates the reflectance.

As shown in FIGS. 7A and 7B, a multilayer with the silicon oxide film 8and the silicon nitride film 9 is formed in the second surface side ofthe semiconductor substrate 1, and the thicknesses of the both films arerespectively adjusted. Consequently, due to the multiple interferenceeffect of light, the transmittance higher than when only using thesilicon oxide film 8 can be obtained. In examples shown in FIGS. 7A and7B, the transmittance of 90 to 98% can be obtained in visible light.

By an adjustment of the thicknesses of the silicon oxide film 8 and thesilicon nitride film 9, various transmittance characteristics can beobtained. For example, the solid-state imaging device is demanded toincrease the light sensitivity of short wavelength side in visiblelight, namely, in a wavelength range from blue (450 nm) to green (540nm). The examples shown in FIGS. 7A and 7B are one of examples of thesuitable thickness for increasing the transmittance of such shortwavelength side to improve the light sensitivity.

FIG. 8 is a view showing a measured result of the transmittance whenforming the multilayer with the silicon oxide film 8 and the siliconnitride film 9 which have various thicknesses respectively. In FIG. 8,an ordinate indicates the thickness of the silicon oxide film 8 and anabscissa indicates the thickness of the silicon nitride film 9. In FIG.8, considering an improvement of the light sensitivity in the shortwavelength side, the transmittance (%) of blue light (450 nm) and greenlight (540 nm) are indicated in the respective thicknesses.

As shown in FIG. 8, by selecting the thickness of the silicon oxide film8 in a range of 15 to 40 nm and the thickness of the silicon nitridefilm 9 in a range of 20 to 50 nm, the transmittance over 90% can beobtained in mostly case. Note that, in these ranges, a combination ofthe suitably thicknesses is selected.

If considering only the improvement of the transmittance, thethicknesses of the silicon oxide film 8 and the silicon nitride film 9may be out of above ranges. However, in the present embodiment, thesilicon oxide film 8 makes charges pass to the silicon nitride film 9,and the silicon nitride film 9 stores the charges.

Therefore, in terms of a passage of electrons, the silicon oxide film 8is preferably no more than 40 nm. Further, depending on a relationshipof the thickness of the silicon nitride film 9 to be used, in order toobtain a high transmittance, it is preferably no less than 15 nm(referred to FIG. 8).

Further, in order to effectively generate the hole storage layer 10 inthe back surface of the semiconductor substrate 1, the silicon nitridefilm 9 preferably stores electrons in the vicinity of the interface ofthe silicon oxide film 8. Namely, if the thickness of the siliconnitride film 9 is too thick, a spatial distribution of the electrons tobe stored may spread, so that the hole storage layer 10 is not able toeffectively generate in the semiconductor substrate 1. Therefore, thethickness of the silicon nitride film 9 is preferably no more than 50nm. Further, in order to obtain the high transmittance, the thickness ofthe silicon nitride film 9 is preferably no less than 20 nm (referred toFIG. 8).

As described above, according to the solid-state Imaging device of thepresent embodiment, the hole storage layer 10 can be generated in theinterface between the semiconductor substrate 1 and the silicon nitridefilm 8 to suppress the occurrence of the dark current to thereby improvethe light sensitivity.

Similarity, by generating the hole storage layer 10, the quantumefficiency loss can be suppressed in the back surface of thesemiconductor substrate 1, a color blend and a persistence of vision canbe suppressed, and the high light sensitivity can be realized.

The silicon nitride film 9 is stacked on the silicon oxide film 8 andthe both thicknesses are adjusted, so that due to the multipleinterference effect of light, the transmittance of the visible light canbe improved in comparison with using only the silicon oxide film 8 toimprove the light sensitivity. For example, the transmittance over 90%can be secured in the vicinity of visible light, and the lightsensitivity can be improved with 25% in comparison with using only thesilicon oxide film 8.

The above solid-state imaging device can be used to, for example, avideo camera, a digital steal camera, an electric endoscope camera orother camera.

FIG. 9 is a view of a configuration of a camera used with the abovesolid-state imaging device.

A camera 30 has the solid-state imaging device 31, an optical system 32,a drive circuit 33, and a signal processing circuit 34. The solid-stateimaging device 31 is the back illuminated solid-state imaging deviceaccording to the present embodiment.

The optical system 32 makes imaging light from a subject, namelyincidence light, focus on an imaging surface (second surface) of thesolid-state imaging device 31. Consequently, in the respective lightreceiving unit 4 of the solid-state imaging device 31, the incidencelight is converted to the signal charges corresponding to an amount ofthe incidence light. And in the n-type semiconductor region 2, thesignal charge is stored for a predetermined period.

The drive circuit 33 supplies various drive signals to the solid-stateimaging device 31. Consequently, the signal charges stored in therespective n-type semiconductor regions 2 of the solid-state imagingdevice 31 are read out. Further, by this drive, a signal is output fromthe solid-state imaging device 31.

The signal processing circuit 34 performs various signal processing toan output signal from the solid-state imaging device 31. After thesignal processing by the signal processing circuit 34, the output signalis stored in a memory or other storage media.

In this way, by applying the solid-state imaging device described aboveto the camera 30 such as a video camera or a digital steal camera, itcan be realized with the camera in which the light sensitivity can beimproved, the dark current can be suppressed and the quantum efficiencycan be improved. As a result, the camera improved with an image qualitycan be realized.

The present invention is not limited to the above embodiment.

If a hole is used as the signal charge, the hole may be stored in theinterface between the silicon oxide film 8 and the silicon nitride film9 and in the silicon nitride film 9 to generate the electron storagelayer at the back surface of the semiconductor substrate 1. And, if thehole is used as the signal charge, polarities of various semiconductorregions may be reversed. Further, in the present embodiment, the examplein which the silicon oxide film 8 is used as the first insulation filmand the silicon nitride film 9 is used as the second insulation film isdescribed, but other insulation films may be used and other impuritiesmay be injected. If employing other insulation films, relatively, thesecond insulation film may have a refractive index higher than the firstinsulation film.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors in so far as they arewithin scope of the appeared claims or the equivalents thereof.

1. A method of producing a solid-state imaging device comprising thesteps of: forming a light receiving unit and a pixel circuit in a firstsurface side of a substrate; grinding a second surface side of saidsubstrate to make said substrate thinner; forming a transparent firstinsulation film on said second surface of said substrate; forming asecond insulation film on said first insulation film; and injectingcharges having the same polarity as a signal charge in an interfacebetween said first insulation film and said second insulation film or insaid second insulation film, wherein, in the steps of forming said firstinsulation film and said second insulation film, said first insulationfilm and said second insulation film are formed to have thicknesses soas to obtain a transmittance of an incidence light higher than whenusing only said first insulation film and wherein the light receivingunit extends only partially into said substrate from the first surfaceside of the substrate towards the second surface side of said substrate.2. A method of producing a solid-state imaging device as set forth inclaim 1, after the step of forming said second insulation film, furthercomprising a step of forming a protection film on said second insulationfilm, said protection film preventing a charge from spreading tooutside, and said charge being retained in an interface of said firstinsulation film and said second insulation film or in said secondinsulation film.
 3. A method of producing a solid-state imaging deviceas set forth in claim 1, wherein, in the step of injecting said charges,a charged electrode is opposed to said second surface side of saidsubstrate.
 4. A method of producing a solid-state imaging device as setforth in claim 1, wherein, in the step of injecting said charges, lightis irradiated to said second surface side of said substrate.
 5. A methodof producing a solid-state imaging device as set forth in claim 1,wherein, in the step of forming said first insulation film, a siliconoxide film is formed.
 6. A method of producing a solid-state imagingdevice as set forth in claim 1, wherein, in the step of forming saidsecond insulation film, a silicon nitride film is formed.